Fabrics comprising blends of cotton with polyester fibers are of considerable commercial importance because of their widespread use in apparel. However, such fabrics are highly flammable. To reduce the flammability of such blends, a flame retardant must be applied to the fabric. A flame retardant is a substance which increases the resistance of a substrate to burning or charring. Flame retardants are known for 100 percent cotton fabrics, but researchers in this field have concluded that the flammability of blend fabrics cannot be predicted from knowledge of the flammability of fabrics made from a single fiber, G. C. Tesoro, Status and Prospects for Flame Resistant Polyester/Cellulose Blend Fabrics, National Bureau of Standards Report COM-73-11265, March, 1973. One important reason for this unpredictability of blend fabrics, e.g., cotton/polyester blends, is the so-called "grid" or "scaffold" effect by which one component of the blend forms a supporting matrix for continued burning of the other component. With regard to this effect, W. Kruse reported:
"In all textile mixtures containing a component capable of forming a structural network (e.g. cotton) and a thermoplastic component (e.g. polyester) account must be taken of the scaffold effect, as it substantially alters the combustion behavior of thermoplastic synthetic fibers. PA0 "In mixed textiles the framework is built in all cases by organic material. Interestingly enough, it is also possible to arrive at a scaffold effect with inorganic material if, for instance, single component fabrics of thermoplastic fibers are given a framework forming finish (e.g. silicate)." W. Kruse, Melliand Textilber, April 1969, pp. 460-469 (Gottlieb Duttweiler Institute Publication No. 45, pp. 137-161, 1969), Combustibility and Flame Resistant Finishing of Mixed Textiles. PA0 1. Fabric PA0 2. treating Solution PA0 3. Drying and Curing Conditions PA0 4. MPDA Efficiency PA0 5. Vertical Flame Test
In accordance with existing technology, polyester fibers can be flame retarded. In one method, a brominated component, tetrabromobisphenol-A ethoxylate, is incorporated in the polymerization reaction producing the polyester from which the fiber is spun. In another method, a polyester fiber is treated topically with an aqueous dispersion of tris-(2,3-dibromopropyl)phosphate which, at elevated temperature, undergoes a thermally induced diffusion into the polyester fiber, thereby reducing the flammability of the fiber.
Polyester fibers having tetrabromobisphenol-A ethoxylate incorporated therein or treated with tris-(2,3-dibromopropyl)phosphate are themselves flame retardant, but when blended with cotton the fire retardance of the polyester is insufficient to render the blend flame retardant. It has now been found that treatment according to the present method significantly increases the resistance of such blends of cotton/flame retardant polyester fibers to flame and provides a material which is significantly more flame retardant than presently known materials.